1. Field of the Invention
The present invention relates to a dot-matrix liquid crystal display apparatus, and more particularly, to a drive circuit for driving a liquid-crystal display panel, thereby to display characters and images in the form of dot-matrix patterns.
2. Description of the Related Art
Conventional liquid-crystal display panels, for displaying characters in the form of dot-matrix patterns having a sealed panel, comprise a front glass plate and a back glass plate which oppose each other across a narrow space filled with liquid crystal. A number of strip-shaped column electrodes are arranged parallel to one another on the inner surface of the front glass plate, and a number of strip-shaped row electrodes are arranged parallel to one another and at right angles to the column electrodes, on the inner surface of the back glass plate, in rows and columns, on the inner surface of the front glass plate. Those portions of the liquid crystal, which are located at the intersections of the column electrodes and the row electrodes function as pixels. Hence, the pixels are arranged in a matrix pattern, that is, in rows and columns.
FIG. 8 shows a conventional dot-matrix liquid crystal display apparatus having a typical structure. The display apparatus has a liquid-crystal display panel 60 filled with liquid crystal and having a number of column electrodes 61l to 61n extending in the vertical direction, and a number of row electrodes 62l to 62m extending in the horizontal direction and, hence, at the right angle to the column electrodes 61l to 61n. Those portions of the liquid crystal which are located at the intersections of the column electrodes 61l to 61n and the row electrodes 62l to 62m function as pixels. Needless to say, the pixels are arranged in a matrix pattern, that is, in rows and columns.
A pair of tape-automated bonding (TAB) films 631 and 632 are secured to the upper edge of the display panel 60. Semiconductor LSI chips 641 and 642, both designed for use in liquid crystal display devices, are mounted on these TAB films 631 and 632, respectively. Either LSI chip has output terminals which are connected to the column electrodes 61l to 61n by wires Pl to Pn arranged on the TAB films. Hence, drives signals can be supplied from the output terminals to the column electrodes 61l to 61n. The LSI chips 641 and 642 can store the display data supplied from an external source and can convert the data into signals for driving the pixels.
Let us assume that there are 24 column electrodes. In this case, the LSI chip 641 outputs 12 pixel data items for the first twelve of the 24 pixels forming one display line, to the first twelve of the 24 column electrodes which are located on the left-half part of the display screen. And, the LSI chip 642 outputs puts 12 pixel data items for the remaining twelve pixels forming the display line, to the remaining twelve column electrodes which are located on the right part of the display screen.
As is shown in FIG. 8, the liquid crystal display apparatus further comprises a liquid-crystal drive circuit 65. This circuit 65 is designed to supply timedivision drive signals having different phases to the row electrodes 62l to 62m, such that a different potential corresponding to the voltage of the drive signal supplied to each row electrode is applied to the pixels defined by this row electrode and the column electrodes 61l to 61n.
Since the wires Pl to Pn connected to the column electrodes 61l to 61n are arranged on the TAB film 631 and 632, both which are secured to the upper edge of the display panel 60, the pitch at which they are placed is inevitably short. Obviously, the more column electrodes, arranged horizontally to display higher-quality images, the shorter the pitch, the higher the manufacturing cost of the apparatus, and the lower the reliability thereof.
This problem is solved by the conventional system illustrated in FIG. 9. As is shown in FIG. 9, the system has a display panel 60 which is identical to that one shown in FIG. 8. TAB films 631 and 632, on which LSI chips 641 and 642 are mounted, are secured to the upper and lower edges a display panel 60, respectively. Signals are supplied from the LSI chip 641 to the odd-numbered column electrodes arranged on the panel 60, whereas signals are supplied from the LSI chip 642 to the even-numbered column electrodes. The wires connected to either LSI chip are, thus, arranged at a relatively long pitch.
The system shown in FIG. 9 has data switching circuit 66 and a CPU (not shown). The circuit 66 receives dot-matrix display data items from an external source. Under the control of the CPU, the circuit 66 distributes the data items, alternately to the LSI chip 641 and the LSI chip 642. This distribution of data items should be performed at high speed, and the CPU cannot control the switching circuit 66 appropriately unless it is a high-performance CPU.